1. Field of the Invention
The present invention relates to an improved method and apparatus for producing a reinforced composite prepreg material. More particularly, the invention relates to a method and apparatus of manufacturing a reinforced polymer matrix composite material by utilizing discontinuous fibers which are embedded in the composite material in the Z-direction.
2. Discussion of the Prior Art
There are currently a number of commercial and defense manufacturing companies that are laminating composite prepreg plies (sheets of uncured resin impregnated onto either continuous or discontinuous reinforcement fibers) to form composite prepreg materials for the manufacturing of composite structures in the aerospace and automotive industry. These types of continuous or alternatively discontinuous composite prepreg materials are typically composed of approximately forty percent cured resin matrix to sixty percent fiber material with the fibers being oriented in the x-y plane or in-plane of the resin matrix.
It is known that these types of composite prepreg materials formed by current manufacturing techniques have a defect in common, namely, weakness in transverse tensile strength and interlaminar shear and peel strength due to the lack of reinforcement fibers in a direction perpendicular to the plane of the fibers. In order to overcome this disadvantage, prior art manufacturing processes have been developed for implanting transversely oriented fibers in the composites. However, the prior art implantation process results in breakage to the in-plane fibers and subsequently reduces in-plane strength. This reduction in in-plane strength limits the transverse fiber volume using the prior art process to two percent.
Other prior art improves transverse strength in polymer composite materials by utilizing three dimensional fiber weaves which are subsequently impregnated with resin using manufacturing processes such as resin transfer molding. These 3D weaves are costly and do not offer the manufacturing flexibility of composite prepreg.
Therefore, a need exists to provide a low cost method to reinforce composite prepreg materials by implanting transversely oriented single fiber filaments without breaking the in-plane fibers and simultaneously achieving high transverse fiber volumes thereby improving the interlaminar strength and damage tolerance of composite prepreg materials.
The subject invention herein solves all of these problems in a new and unique manner which has not been part of the art previously. Some related patents are described below:
U.S. Pat. No. 4,613,784 issued to M. Haun et al., on Sep. 23, 1986.
This patent describes a piezoelectric PZT-polymer composite of 1-3 and 1-3-0 connectivity which is transversely reinforced with glass fibers to increase the hydrostatic piezoelectric charge and voltage coefficients for possible use in hydrophone applications.
U.S. Pat No. 4,328,272 issued to M. Maistre on May 4, 1982
This patent is directed to a structure comprising a stack of superimposed layers of bi-dimensional reinforcing material and rectilinear elements located transversely through the stack with each reinforcing element being at an angle with the plane that is tangential to the layers it transverses.
While the basic concepts presented in the aforesaid patents are desirable, the methods employed by each for Z-direction reinforcement are limited by the materials used to achieve the desired result and furthermore do not provide for simultaneously enhancing the structural, thermal and electrical conductivity of the material.